What is the difference between the two types of outlets?

Modern, grounded 120-volt receptacles, also referred to as outlets, in North America have a small, round ground slot centered below two vertical hot and neutral slots, and it provides an alternate path for electricity that may stray from the appliance.

Since the early 1960s, most electrical codes have required a ground wire to be run to all outlets and appliances.  Prior to that time, most wiring was just two wires (hot and neutral).  The ground wire provides an alternate path for electricity that may stray from an appliance or product to make its way safely back to the breaker or fuse box and exit the building into the main ground connection.

If the home was built before 1960, it likely has as least some two-prong ungrounded outlets, although some may have been upgraded to grounded outlets.  Since 1962, the National Electrical Code has required three-prong outlets for all new homes.

Most residential electrical outlets are connected to circuits of 120 volts.  If more energy than that runs through the wire, the risk of a fault increases.  This is why overloading outlets by plugging in too many appliances is a bad idea…and it’s an even bigger risk if you overload a ungrounded outlet.

Watch out for deterioration of wires and their protective insulation.  A short circuit in the receptacle wiring, combined with ungrounded outlets typically found in older houses is a recipe for potential fire and injury.

Why are grounded outlets important?

To understand the why, you have to understand what a grounded outlet does.  The two vertical slots represent both a “hot” wire and a “neutral” wire.  The ground wire in a grounded outlet ties into the neutral vertical slot.  Why the redundancy?  It acts like a failsafe.  Should anything go awry with an outlet, such as a short, the electricity simply travels safely along the ground wire back to the panel.  Without the ground wire, that electricity can channel into materials such as fabrics located close to the outlet or a very unlucky person.

Can a two-slot outlet simply be replaced with a three-slot receptacle?

Replacing a two-slot outlet with a three-slot outlet without rewiring the electrical system may serve as a seemingly proper outlet for three-pronged appliances; however, this “upgrade” is potentially more dangerous because the outlet will appear to be grounded and future homeowners might never be aware that their system is not grounded.  By rule of thumb, if a building still uses knob-and-tube wiring, it is likely that any three-slot outlets are ungrounded.

How can ungrounded outlets be upgraded safely?

Upgrading the electrical system can be accomplished in one of the following ways:

  1. Install three-slot outlets and wire them so that they are correctly grounded. This means that all new outlets will require running new wire from the outlet back to the main panel.  This is the most expensive option.
  2. Install a junction box close to the main panel (the junction box must be accessible at all times). The equipment bonding conductors in the junction box must be properly connected to an equipment grounding conductor sized for the circuit that terminates on a grounding busbar in a subpanel, or the neutral busbar at the main panel to ensure that this method is code compliant. New wiring can be run from the junction box to the outlets that require upgrading. A junction box is the proper way of “splicing” wire without any concern for safety.  This option is also costly to integrate.
  3. Install ground-fault circuit interrupters (GFCIs). These can be installed upstream or at the outlet itself.  This is a good option for ungrounded outlets located in damp areas such as bathrooms, kitchens, or garages.  The outlet will still be ungrounded but a GFCI will automatically “trip” the circuit (shutting off electrical flow) in the event of a power surge.  GFCIs are an accepted replacement because they will protect against electric shocks even in the absence of grounding, but they may not protect the powered appliance.  Furthermore, GFCI-protected outlets may not work effectively with surge protectors.  Ungrounded GFCI-protected outlets should be identified with labels that come with the new outlet that state: “No Equipment Ground”.  This is by far the most popular and cost-effective method of ensuring that appliances that require a grounded outlet can be plugged in safely.

Is it necessary to replace each outlet with a GFCI or just the first one on the circuit?

The first outlet on the circuit will provide protection for all outlets upstream.  However, it is important to note that one must properly identify which outlet is first on the circuit.

Also keep in mind that many electrical devices can be plugged into an ungrounded outlet: small kitchen appliances, lamps, radios, etc.

Furthermore, a recent change to the electrical code in 2018 states that a dedicated circuit to supply more than one refrigerator outlet is now permitted.  The code has been revised to more clearly state that the requirement only applies to receptacles mandated by 26-712(d)(i) for refrigerators in kitchens. The requirement does not apply to refrigerators installed in other locations.

If anything, remember this:

  • You CANNOT ground an ungrounded outlet without running new wire.
  • Each individual ungrounded outlet must be upgraded separately.
  • GFCIs can be installed at the first outlet on the circuit and will provide some fault protection but do not protect the appliances nor do they work effectively with surge protectors. These outlets MUST be identified as “No Equipment Ground”.
  • Hire a licensed electrician to do the job properly.

For more information on GROUNDED circuits, please refer to our article by clicking here